Fuel fragmentation and relocation (FFR) model in SPACE code PART 2: Validation and sensitivity analyses

The new ECCS regulations were recently considered in South Korea. One of the major concerns in this revision is the consideration of fuel fragmentation, relocation, and dispersal (FFRD) phenomena during a loss of coolant accident (LOCA). In response, the FFR model was newly implemented in the SPACE code, which is a safety analysis code. The FFR model based on the QT model, which was developed by Quantum Technology Corporation, was developed with a threshold size of fuel fragments for fuel relocation, fuel power distribution, and so on. In this study, to validate the newly developed FFR model in SPACE code, calculations using Halden IFA-650 tests are conducted. Overall, the results show that the newly developed FFR model yields results that are consistent with experimental results in terms of fuel relocation and their effects on cladding temperature. However, when the cladding deformation is not well predicted, the fuel relocation prediction is poor. Thus, the cladding deformation is the most critical parameter for the FFR phenomena. In addition, for a fresh fuel condition, the threshold fragment size is additionally proposed in the fuel relocation model. For a better understanding of the FFR model behavior during a LOCA, some sensitivity tests for major FFR model parameters are conducted. This can give valuable information to develop FFR modeling in safety analysis methodology.